Abstract
A detailed numerical study of propagation characteristics of a coupled wedge plasmon polariton (CWPP) in splitted groove waveguide (SGW) formed with two metal wedges is performed by using the finite element method (FEM). It is shown that the SGW structure could confine CWPP modes tightly to the nano-gap region between the wedge tips, operating in a much broad bandwidth. The effect of the glass substrate, wedge roundness, gap width, groove wedge angle, and groove depth are also investigated. Particularly, our SGWs are found to be quite robust against groove depth reduction, which could be beneficial to minimize the waveguide structure dimensions. Feasibility of using such SGWs for the design of efficient subwavelength plasmonic elements is also discussed on the nanoscale whispering gallery resonators as an example.
Highlights
Surface plasmon polariton (SPP) is a fundamental electromagnetic excitation which may exist at the interface between metal and dielectric, with the fields decaying exponentially away from its maximum at the interface [1]
When a trapezoid shaped gap instead of a rectangular gap is introduced into a metal film, the formed structure - a splitted groove waveguide (SGW) can support highly confined coupled wedge plasmon polariton (CWPP) modes due to its reduced symmetry, which will be demonstrated later in the text
We have numerically investigated the propagation characteristics of the supposed SGW as an optional prototype of the plasmonic waveguide structure
Summary
Surface plasmon polariton (SPP) is a fundamental electromagnetic excitation which may exist at the interface between metal and dielectric, with the fields decaying exponentially away from its maximum at the interface [1]. V-grooves engraved in a thick metal film supporting channel plasmon polartions (CPPs) have been demonstrated to show strong lateral confinement of the SPP fields at the bottom of grooves, simultaneously with low propagation losses at telecommunication wavelengths [13] Based on such kind of V-groove waveguide (VGW) structure, plasmonic functional devices such as ring resonators, MachZehnder interferometers, and add-drop multiplexers, have been successfully realized [15, 16]. When a trapezoid shaped gap instead of a rectangular gap is introduced into a metal film, the formed structure - a splitted groove waveguide (SGW) can support highly confined coupled wedge plasmon polariton (CWPP) modes due to its reduced symmetry, which will be demonstrated later in the text. Compared to the case of the WGR using conventional VGW in Ref. 23, it is shown that very slight operation wavelength shift can be obtained in the ring resonator based on SGWs due to the negligible cross talk effect over the resonator disk
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